Re: [PATCH 3/6] drm: fourcc byteorder: add bigendian support to drm_mode_legacy_fb_format

From: "Michel Dänzer" <michel@daenzer.net>
To: Gerd Hoffmann <kraxel@redhat.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>,
	dri-devel@lists.freedesktop.org,
	open list <linux-kernel@vger.kernel.org>,
	amd-gfx@lists.freedesktop.org
Subject: Re: [PATCH 3/6] drm: fourcc byteorder: add bigendian support to drm_mode_legacy_fb_format
Date: Thu, 27 Apr 2017 09:52:59 +0900	[thread overview]
Message-ID: <6bd62182-0de5-a8a7-78c3-029fc73ecc91@daenzer.net> (raw)
In-Reply-To: <1493208671.23739.19.camel@redhat.com>

On 26/04/17 09:11 PM, Gerd Hoffmann wrote:
>   Hi,
> 
>>>> Just to reiterate, this won't work for the radeon driver, which programs
>>>> the GPU to use (effectively, per the current definition that these are
>>>> little endian GPU formats) DRM_FORMAT_XRGB8888 with pre-R600 and
>>>> DRM_FORMAT_BGRX8888 with >= R600.
>>>
>>> Hmm, ok, how does bigendian fbdev emulation work on pre-R600 then?
>>
>> Using a GPU byte swapping mechanism which only affects CPU access to
>> video RAM.
> 
> That is done using the RADEON_TILING_SWAP_{16,32}BIT flag mentioned in
> another thread?

Right.

> What about dumb bos?  You've mentioned the swap flag isn't used for
> those.  Which implies they are in little endian byte order (both gpu and
> cpu view).

Right, AFAICT from looking at the code.

> Does the modesetting driver work correctly on that hardware?

Not sure.

-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer